Homeodomain-interacting protein kinase maintains neuronal homeostasis during normal Caenorhabditis elegans aging and systemically regulates longevity from serotonergic and GABAergic neurons
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eLife assessment
This fundamental study substantially advances our understanding of how aging and stress resilience across an organism is determined by identifying a new player in this process and uncovering its mode of action. The evidence is solid as the methods, data and analyses broadly support the claims with only minor weaknesses. The work will be of broad interest to the field of aging and protein homeostasis.
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Abstract
Aging and the age-associated decline of the proteome is determined in part through neuronal control of evolutionarily conserved transcriptional effectors, which safeguard homeostasis under fluctuating metabolic and stress conditions by regulating an expansive proteostatic network. We have discovered the Caenorhabditis elegans homeodomain-interacting protein kinase (HPK-1) acts as a key transcriptional effector to preserve neuronal integrity, function, and proteostasis during aging. Loss of hpk-1 results in drastic dysregulation in expression of neuronal genes, including genes associated with neuronal aging. During normal aging hpk-1 expression increases throughout the nervous system more broadly than any other kinase. Within the aging nervous system, hpk-1 induction overlaps with key longevity transcription factors , which suggests that hpk-1 expression mitigates natural age-associated physiological decline. Consistently, pan-neuronal overexpression of hpk-1 extends longevity, preserves proteostasis both within and outside of the nervous system, and improves stress resistance. Neuronal HPK-1 improves proteostasis through kinase activity. HPK-1 functions cell non-autonomously within serotonergic and γ-aminobutyric acid (GABA)ergic neurons to improve proteostasis in distal tissues by specifically regulating distinct components of the proteostatic network. Increased serotonergic HPK-1 enhances the heat shock response and survival to acute stress. In contrast, GABAergic HPK-1 induces basal autophagy and extends longevity, which requires mxl-2 (MLX), hlh-30 (TFEB), and daf-16 (FOXO). Our work establishes hpk-1 as a key neuronal transcriptional regulator critical for preservation of neuronal function during aging. Further, these data provide novel insight as to how the nervous system partitions acute and chronic adaptive response pathways to delay aging by maintaining organismal homeostasis.
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Author Response
Reviewer #1 (Public Review):
The goal of the authors was to understand how the kinase, hpk-1, could regulate and interrogate different aspects of cellular stress resilience. To this end, the authors uncovered that hpk-1 is coexpressed with several transcription factors known to regulate different stress responses and this coregulation only appears to occur in the nervous system. Taking a deeper dive, they convincingly find that hpk-1 overexpression in either serotonergic of GABAergic neurons can protect animals from heat stress or toxic protein aggregates. Interesting, it appears that hpk-1 functions in serotonergic neurons differently from GABAergic neurons in the induction of the heat shock response and autophagy.
Overall, the experiments and results are solid and the conclusions drawn reflect the result. The …
Author Response
Reviewer #1 (Public Review):
The goal of the authors was to understand how the kinase, hpk-1, could regulate and interrogate different aspects of cellular stress resilience. To this end, the authors uncovered that hpk-1 is coexpressed with several transcription factors known to regulate different stress responses and this coregulation only appears to occur in the nervous system. Taking a deeper dive, they convincingly find that hpk-1 overexpression in either serotonergic of GABAergic neurons can protect animals from heat stress or toxic protein aggregates. Interesting, it appears that hpk-1 functions in serotonergic neurons differently from GABAergic neurons in the induction of the heat shock response and autophagy.
Overall, the experiments and results are solid and the conclusions drawn reflect the result. The model suggests that the receiving cell deciphers that either heat shock response or autophagy can be induced in the same cell, but the data suggest otherwise. Perhaps the model should be reworked to reflect this point.
We thank the reviewer for their kind assessment and suggestion to refine our model. Indeed, we did not intend to imply that that the receiving cell/tissues were the same after each stimulus, but were attempting to simplify the diagram and condense space. In the revised manuscript we have altered the model (Figure 9B) to reflect that the recipient tissues are distinct.
Reviewer #2 (Public Review):
Lazaro-Pena et al. investigated how a conserved kinase called homeodomain interacting protein kinase (HPK-1), helps to preserve neuronal function, motlity and stress resilience during aging in the metazoan, C. elegans. HPK-1 is a member of the HIPK kinases that, in mammalian systems, regulate the activity of transcription factors (TFs), chromatin modifiers, signaling molecules and scaffolding proteins in response to cellular stress. The group finds that in C. elegans, HPK-1 depletion causes a premature shortening of lifespan and decreases motility and stress resilience in the whole animal. Conversely, increasing active, but not enzymatically dead, HPK-1 levels in the nervous system alone is sufficient to extend lifespan and mitigate the accumulation of aging-associated protein aggregates. The authors then identify a subset of neurons and cell stress response pathways that could be responsible for the contribution of HPK-1 to lifespan and neuronal health. This leads the authors to propose a hypothesis whereby HPK-1 activity in specific neurons preserves protein homeostasis and neuronal integrity, and thus limits the aging-induced decline in organismal function.
Overall, the authors test several functional readouts for neuronal activity to support their claim that HPK-1 activity limits functional decline during aging. These experiments are solid, and the use of a kinase dead HPK-1 in these experiments adds strong support to their claim that HPK-1 activity preserves organismal health. However, weaknesses in the experimental layout and rigor, and the statistical analyses of the publicly available data, limit the inferences that can be made, and further experimental evidence would be required to confirm the working model proposed by the authors.
We thank the reviewer for their thoughtful and balanced assessment of our study.
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eLife assessment
This fundamental study substantially advances our understanding of how aging and stress resilience across an organism is determined by identifying a new player in this process and uncovering its mode of action. The evidence is solid as the methods, data and analyses broadly support the claims with only minor weaknesses. The work will be of broad interest to the field of aging and protein homeostasis.
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Reviewer #1 (Public Review):
The goal of the authors was to understand how the kinase, hpk-1, could regulate and interrogate different aspects of cellular stress resilience. To this end, the authors uncovered that hpk-1 is co-expressed with several transcription factors known to regulate different stress responses and this co-regulation only appears to occur in the nervous system. Taking a deeper dive, they convincingly find that hpk-1 overexpression in either serotonergic of GABAergic neurons can protect animals from heat stress or toxic protein aggregates. Interesting, it appears that hpk1 functions in serotonergic neurons differently from GABAergic neurons in the induction of the heat shock response and autophagy.
Overall, the experiments and results are solid and the conclusions drawn reflect the result. The model suggests that the …
Reviewer #1 (Public Review):
The goal of the authors was to understand how the kinase, hpk-1, could regulate and interrogate different aspects of cellular stress resilience. To this end, the authors uncovered that hpk-1 is co-expressed with several transcription factors known to regulate different stress responses and this co-regulation only appears to occur in the nervous system. Taking a deeper dive, they convincingly find that hpk-1 overexpression in either serotonergic of GABAergic neurons can protect animals from heat stress or toxic protein aggregates. Interesting, it appears that hpk1 functions in serotonergic neurons differently from GABAergic neurons in the induction of the heat shock response and autophagy.
Overall, the experiments and results are solid and the conclusions drawn reflect the result. The model suggests that the receiving cell deciphers that either heat shock response or autophagy can be induced in the same cell, but the data suggest otherwise. perhaps the model should be reworked to reflect this point.
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Reviewer #2 (Public Review):
Lazaro-Pena et al. investigated how a conserved kinase called homeodomain interacting protein kinase (HPK-1), helps to preserve neuronal function, motlity and stress resilience during aging in the metazoan, C. elegans. HPK-1 is a member of the HIPK kinases that, in mammalian systems, regulate the activity of transcription factors (TFs), chromatin modifiers, signaling molecules and scaffolding proteins in response to cellular stress. The group finds that in C. elegans, HPK-1 depletion causes a premature shortening of lifespan and decreases motility and stress resilience in the whole animal. Conversely, increasing active, but not enzymatically dead, HPK-1 levels in the nervous system alone is sufficient to extend lifespan and mitigate the accumulation of aging-associated protein aggregates. The authors then …
Reviewer #2 (Public Review):
Lazaro-Pena et al. investigated how a conserved kinase called homeodomain interacting protein kinase (HPK-1), helps to preserve neuronal function, motlity and stress resilience during aging in the metazoan, C. elegans. HPK-1 is a member of the HIPK kinases that, in mammalian systems, regulate the activity of transcription factors (TFs), chromatin modifiers, signaling molecules and scaffolding proteins in response to cellular stress. The group finds that in C. elegans, HPK-1 depletion causes a premature shortening of lifespan and decreases motility and stress resilience in the whole animal. Conversely, increasing active, but not enzymatically dead, HPK-1 levels in the nervous system alone is sufficient to extend lifespan and mitigate the accumulation of aging-associated protein aggregates. The authors then identify a subset of neurons and cell stress response pathways that could be responsible for the contribution of HPK-1 to lifespan and neuronal health. This leads the authors to propose a hypothesis whereby HPK-1 activity in specific neurons preserves protein homeostasis and neuronal integrity, and thus limits the aging-induced decline in organismal function.
Overall, the authors test several functional readouts for neuronal activity to support their claim that HPK-1 activity limits functional decline during aging. These experiments are solid, and the use of a kinase dead HPK-1 in these experiments adds strong support to their claim that HPK-1 activity preserves organismal health. However, weaknesses in the experimental layout and rigor, and the statistical analyses of the publicly available data, limit the inferences that can be made, and further experimental evidence would be required to confirm the working model proposed by the authors. -